Preliminary Observations on the Ability of Hyperspectral Imaging to Provide Detection and Visualization of Bloodstain Patterns on Black Fabrics

Abstract

The analysis of bloodstain patterns can assist investigators in understanding the circumstances surrounding a violent crime. Bloodstains are routinely subjected to pattern analysis, which is inherently dependent upon the ability of the examiner to locate and visualize bloodstain patterns on items of evidence. Often, the ability to properly visualize bloodstain patterns is challenging, especially when the stain patterns occur on dark and/or patterned substrates. In this study, preliminary research was performed to better understand how near-infrared reflectance hyperspectral imaging (HSI) could be used to observe bloodstain patterns on commonly encountered black fabrics. The ability of HSI to visualize latent bloodstains on several commonly encountered substrates is demonstrated. The images acquired through HSI are of sufficient quality to allow for differentiation between stains produced from an impact mechanism or a transfer mechanism. This study also serves as a proof of concept in the differentiation of multiple staining materials. Because of its ability to generate spectral data, the data provide a preliminary separation of stains where more than one type of stain existed.

Body Fluids and Spectroscopic Techniques in Forensics: A Perfect Match?

“…In fact, this combination provides both spatial and spectral information of samples enabling the visualization of stains based on their characteristic spectra. However, most of the studies are exclusively focused on blood detection [18][19][20][21][22][23]. For instance, Morgan et al [18,19] identified diluted blood stains on dark fabrics made of acrylic fibre, cotton, nylon and polyester through the contrast between blood and background when using MIR thermal imaging.…”

“…In brief, results again proved the superiority of NIR to detect blood stains except for the "small spatter" stains and most of the substances tested were easily distinguished from blood. Schuler et al [22] overcame these results using a wider NIR range (650-1100 nm and 960-1650 nm) and demonstrated the detection and visualization of both transfer/smear and spatter blood stains on black fabrics (cotton and denim). Furthermore, the discrimination among stains of blood and potential false-positive substances such as lotions and lipsticks was achieved based on their different NIR spectral response.…”

“…Portable hyperspectral cameras working along NIR range have been successfully tested for the detection of blood stains [20][21][22][23]. NIR range is less specific than MIR, but it is selective enough to preliminary identify blood stains.…”

“…With regards to stand-off detection of forensic evidence at crime scene, both HSI, FTIR and Raman portable instruments are available [20][21][22][42][43][44]. For now, portable and miniaturized instruments have been used for detection of drugs and explosives, thanks to the wide available library containing these compounds [42][43][44].…”

“…For example, a large part of the studies were carried out by analysing samples of body fluids on glass slides or directly placed onto the instrument [25,[33][34][35][36][37][38][39][40][41], which is an extremely unusual substrate in real cases. In addition, studies in which stains were prepared on different clothes such as cotton, polyester, acrylic or wool, exclusively correspond to blood [18][19][20][21][22][23]27,30,31] except for studies [24,26]. There are still some unsolved questions concerning the identification of stains of body fluids (particularly semen, vaginal fluid, saliva, urine and sweat) on fabrics, such as the influence of the fabric material and colour to the IR or Raman spectrum.…”